The invention relates to an optical scanning device comprising a light transmitter and a light receiver which are arranged in spatial proximity to one another and which each comprise a deflecting device with which a scanning light beam emitted by a transmitter unit is directable along a transmission path onto an object to be scanned and, after reflection at said object, along a reception path onto a receiving unit.
Such scanning devices serve, for example, as range finders which work according to the principle of light transit time and in which the transmitting unit comprises a laser device.
These systems are characterized by high sensitivity of the light receiver which can be in the range of some nW so that a reliable detection of objects with low degrees of reflection is ensured. The transmitting power of the light transmitter is, in contrast, a plurality of orders of magnitude higher and can be, for example, in the range of some mW to some W.
It is a problem with such systems that measures are required, in particular due to the high sensitivity of the light receiver in comparison with the transmitting power, to avoid the system blinding itself, i.e. to prevent light transmitted from the light transmitter which is not reflected from the object to be scanned, but from other objects, from being detected by the receiver unit. Known sources for such interfering scattered light include, for example, the front plates provided for the passage of light, which result in a disadvantageous scattering of the transmitted light, in particular in a dirty state. It is in particular problematic that self-blinding of the system can result in saturation effects of the receiver electronics which make it impossible to measure the light transit time with a high temporal resolution.
It is an object of the invention to provide an optical scanning device of the kind initially mentioned in which self-blinding is reliably avoided and which, at the same time, has the simplest possible design.
This object is satisfied in accordance with the invention starting from an optical scanning device of the kind initially mentioned by the transmission path and the reception path being optically separated from one another in the region of the light transmitter and the light receiver.
The possibility of scattered light being able to enter the reception path from the transmission path and resulting in the receiving unit being blinded is excluded by the optical separation between the transmission path and the reception path in the region of the light transmitter and the light receiver. Cross-talk between the transmission path and the reception path can thus be completely avoided in accordance with the invention.
In a preferred embodiment of the invention, the light transmitter and the light receiver are arranged in a common housing, with the transmission path and the reception path being optically separated from one another inside the housing. Said separation is preferably effected by the light transmitter and the light receiver each being arranged in a respective chamber of the housing, with the transmitting chamber and the receiving chamber being separated from one another in a light-tight manner by a partition wall.
The optical separation between the transmitting channel and the receiving channel is hereby effected with very simple design means. The scanning device in accordance with the invention can thus be made at a particularly favorable cost.
The transmitting chamber and the receiving chamber can be closed by a light permeable window. The transmitting unit and the receiving unit can thus be protected against external influences, with scattering effects at the light permeable windows being unproblematic due to the light-tight separation between the transmitting chamber and the receiving chamber.
In a preferred practical embodiment of the invention, a deflecting unit in the form of a mirror wheel drivable to execute a rotary movement is associated with both the transmitting unit and the receiving unit. On the transmitter side, it is possible to generate scanning beams executing a periodic scanning movement with such a mirror wheel, also known as a polygon. Interfering scattered light is effectively avoided by the optical separation in accordance with the invention between the transmitting channel and the receiving channel, in particular with such scanner systems where there was a high potential risk of self-blinding up to now.
It is preferred for both mirror wheels to be drivable to execute a joint rotary movement and to have a common drive shaft guided in a light-tight manner through the dividing wall between the transmitting chamber and the receiving chamber.
In this process, the two mirror wheels arranged at the common drive shaft can be considered as a single deflecting unit in the form of a divided mirror wheel for the whole system, with a transmitting section and a receiving section being completely separated from one another in an optical respect by the partition wall in said deflecting unit. The synchronization of the two mirror wheels or the two sections of the common, divided mirror wheel is ensured in this process by the common rotary movement, while the penetration of interfering scattered light into the reception paths is completely excluded.